Hydration of alpha-Pinene to obtain alpha-terpineol, using an ionic liquid as solvent, which is synthesized from a tertiary amine and an inorganic acid

ABSTRACT

An ionic liquid as a solvent in the hydration reaction of α-pinene to α-terpineol. The ionic liquid is obtained from the reaction of an amine and an inorganic acid. The use of the ionic liquid as solvent favors the selectivity towards the formation of α-terpineol and once the reaction product has been brought to room temperature, the organic phase can be physically separated from the inorganic one by decantation. The inorganic phase contains the ionic liquid, water and reaction catalyst and can be directly reused for a new reaction batch.

OBJECT OF THE INVENTION

The present invention aims to use ionic liquids obtained from tertiaryamines and inorganic acids as solvents in the hydration of α-pinene toα-terpineol. This invention has the advantage over other reportedsystems that the ionic liquid is low cost, it is prepared in a simpleway, by a single step, and that the recovery of the products of thehydration of α-pinene is carried out by separating the two phases thatare obtained by simple decantation. The ionic liquid does not requireany treatment to be reused in the same reaction, as it remains stable.

BACKGROUND

Terpineol is a product used in the perfume industry, in cosmetics, as abase for cleaners, detergents and surfactants for industrialapplications. Although there are various sources of terpineol in anatural way, one of the most used ways to produce it, is the hydrationof α-pinene. The transformation of α-pinene to terpineol has been thesubject of numerous studies and there are several patents on thesubject. Sapp (1953) developed a multi-step process that included theturpentine reaction (whose main component is α-pinene), usingconcentrated sulfuric acid (80% by weight), a second dilution step ofthe reaction mixture, centrifugation, washing with sodium carbonate,washing with water, and boiling with sulfuric acid (0.2 to 0.5 N) toobtain the crude terpineol. Herrlinger's patent (1959) describes thesynthesis of αa-terpineol from α-pinene using sulfuric acid in water asa catalyst, in concentrations of 20 to 40%, and although it involvesfewer steps than the aforementioned patent, this process has a loweryield, and it is necessary to use processes of high energy demand suchas distillation, for the recovery of the product of interest. Inaddition, Herrlinger proposed that to improve the selectivity towardsα-terpineol, some solvents such as hexane and para-cymene should beused, however, the drawback is that a process such as distillation mustbe used to recover said solvent. In Mexico, patents 126774 and 155026describe a process for obtaining terpineol from sulfated turpentine thatis very similar to that of the Sapp patent, since they consist of aprocess that includes the hydration of turpentine using sulfuric acid(25-35% by weight), separation and washing of the product with sodiumcarbonate, steam distillation, boiling with sulfuric acid and washingwith soda.

In the scientific literature, the use of solid catalysts has beenreported to facilitate the separation of the catalyst and the product,however, there is only a history of the use of an ionic liquid in thisreaction, Liu et al. [2008] reported the use of1-methyl-3-(3-sulfopropyl)-imidazolium dihydrogen phosphate ([HSO₃-pmim]H₂PO₄), however, the preparation of this ionic liquid is complex andinvolves high-cost reagents such as 1,3 propane sulfone, 1-methylimidazole, in addition, requires ethyl acetate as a solvent both as areaction medium and for washing 3-(1-methylimidazolium-3-yl)propane-1-sulfonate (MIM-PS), which is an intermediate product in thesynthesis of ([HSO₃-pmim] H₂PO₄). The use of1-methyl-3-(3-sulfopropyl)-imidazolium dihydrogen phosphate ([HSO₃-pmim]H₂PO₄) as ionic liquid concern a process that is unfavorableeconomically, and also from the point of view of caring for theenvironment.

This patent concerns a one-step ionic liquid synthesis method, withlow-cost components and its use in the conversion of α-pinene toα-terpineol, allowing the separation of the products by a physicalmeans, which is the decantation, since at room temperature two clearlydistinguishable phases are formed.

REFERENCES

Asis-Rahais, J., Procedimiento mejorado para la obtención de terpineol,Patente Mx 131,593 (1974).

Garcia-Leal A., Garcia Leal E., Procedimiento de fabricación deterpineol a partir de aguarrás sulfatado, Patente Mx 155,026 (1988).

Herrlinger, R., Production of alpha-Terpineol, U.S. Pat. No. 2,898,380(1959).

Liu, S. W., Yu, S. T., Liu, F. S., Xie, C:X., Li, L., Ji, K. H.,Reactions of α-pinene using acidic ionic liquids as catalysts, J. Molec.Catal. A:Chem. 279 (2008) 177-181.

Sapp, J. E., Production of terpineol U.S. Pat. No. 2,628,258 (1953).

DETAILED DESCRIPTION OF THE INVENTION

The present invention describes a method to produce α-terpineol fromα-pinene, using an ionic liquid as the reaction solvent that favors theselectivity and performance of the conversion of α-pinene toα-terpineol, with the advantage that once the reaction time hasconcluded, the ionic liquid is separated by decantation of the organicphase containing the terpineol and the by-products of the reaction,while the inorganic phase contains the ionic liquid with the catalystused and water. Thus, the inorganic phase at bottom of reactor, can beused again for a new batch just adding α-pinene and the consumed water.

The ionic liquid that has been found to show the best results in thetransformation reaction from α-pinene to α-terpineol is the product ofthe reaction of an inorganic acid with a tertiary amine, such assulfuric acid with tripropylamine, that is tripropylamine acid sulfate.However, this patent is not limited to the use of this ionic liquid,since it was also found that other amines and other acids can be used,such as triethylamine, tributyl amine, triphenyl amine, tri isobutylamine, and in the case of acids, phosphoric acid was also used,obtaining in all cases the formation of α-terpineol with a yieldsuperior to that obtained by not using ionic liquid as a solvent.

For the preparation of the ionic liquid, an equimolar quantity ofsulfuric acid of the highest available purity, preferably 99.5%, isadded slowly and with constant stirring in a suitable containercontaining the required amount of the amine. Depending on the ambienttemperature and the type of amine, it may be necessary to increase thetemperature of the container, since the formation of the ionic liquidleads to a notable increase in viscosity. In order to eliminate theunreacted amine, when there is an excess of it, or the water present inthe sulfuric acid, the mixture is left stirring between 90 and 110° C.until the emission of vapors is not observed.

The ionic liquid once synthesized can be stored until use. To carry outthe reaction of pinene to terpineol, the ionic liquid is poured into thereactor, then the required amount of water is added., The catalyst isslowly poured (sulfuric acid or phosphoric acid) under stirring,verifying that the temperature does not rise uncontrollably.

Once the addition of the catalyst is complete, the reaction temperatureis set. When the reactor is at the reaction temperature, pinene is addedwhile maintaining stirring, and the system is kept under controlledtemperature. Stirring is maintained for the required time to obtain thehighest yield. Once the reaction time has ended, the reactor is allowedto cool to room temperature and later when the separation of the twophases (organic and inorganic) is clear, they are separated bydecantation. The upper phase contains the unreacted pinene and theproducts formed from the pinene, while in the lower part, the mixture ofwater, catalyst and ionic liquid remains. The lower part of the mixtureis transferred back to the reactor to carry out a new reaction. Ifnecessary, the content of water is adjusted before the adding of newpinene load, to start another reaction.

EXAMPLE 1 OF SYNTHESIS OF IONIC LIQUID AMINE-H₂SO₄

60 grams of tripropylamine (TPA) are placed in a suitable container(glass or stainless steel), and 41.6 grams of sulfuric acid (purity98.5% by weight) are added slowly and under constant stirring. Once themixture is finished, the ionic liquid is already formed. If necessary,the temperature of the container can be raised to 100° C., whilemaintaining the stirring. This heating ensures that the water present inany of the reagents used, or the excess of amine is eliminated, in caseof variations in the purity of the reagents. With this procedure 101grams of the ionic liquid are obtained. Hereinafter this ionic liquid iscalled TPAS.

EXAMPLE 2 OF SYNTHESIS OF IONIC LIQUID AMINE-H₂SO₄

60 grams of tripropylamine (TPA) are placed in a suitable container(glass or stainless steel), and 48 grams of phosphoric acid (purity of85.6% by weight) are added slowly and under constant stirring. Once themixture is finished, the ionic liquid is already formed. If necessary,the temperature of the container can be raised to 100° C., whilemaintaining the stirring. This heating ensures that the water present inany of the reagents used, or the excess of amine is eliminated, in caseof variations in the purity of the reagents. With this procedure 101grams of the ionic liquid are obtained. Hereinafter this ionic liquid iscalled TPAP.

EXAMPLE OF SYNTHESIS OF α-TERPINEOL FROM α-PINENE USING TPAS AS SOLVENT

24.1 g of TPAS, 12 g of water and 2 g of H₂SO₄ (purity of 98.5%) are fedinto a reactor, as a last step 10.2 g of α-pinene are added. The mixtureis heated to 70° C. and is kept with constant stirring at thattemperature. The reaction is stopped after four hours of reaction andthe contents of the reactor are cooled to room temperature. The reactionproduct separates into two phases and the upper part contains thereactants and products, while the lower part contains water, the ionicliquid and the catalyst. The analysis of the obtained product indicatesthat the conversion under these reaction conditions and time is 60% withselectivity towards α-terpineol of 41%.

EXAMPLE OF SYNTHESIS OF α-TERPINEOL FROM α-PINENE USING IONIC LIQUIDOBTAINED FROM TRIETHYLAMINE AS SOLVENT AND H₂SO₄ (TEAS)

19.9 g of TEAS, 6 g of water and 1 g of H₂SO₄ (98.5% purity) are fedinto a reactor, as a last step 10.2 g of α-pinene are added. The mixtureis heated to 60° C. and is kept with constant stirring at thattemperature, the reaction is stopped after fifteen hours of reaction andthe contents of the reactor are cooled to room temperature.

The reaction product separates into two phases and the upper partcontains the reactants and products, while the lower part containswater, the ionic liquid and the catalyst. The analysis of the productobtained indicates that the conversion under these reaction conditionsand time is 48% with a selectivity towards α-terpineol of 37%. Theanalysis of lower part shows that the ionic liquid contains water andthe sulfiric acid.

EXAMPLE OF SYNTHESIS OF α-TERPINEOL FROM α-PINENE USING AS SOLVENT THEIONIC LIQUID TPAS AND PHOSPHORIC ACID AS CATALYST

24.1 g of TPAS, 12 g of water and 4.58 g of H₃PO₄ (purity of 85.6%) arefed into a reactor, as a last step 10.2 g of α-pinene are added. Themixture is heated to 70° C. and is kept with constant stirring at thattemperatura. The reaction is stopped after four hours of reaction andthe contents of the reactor are cooled to room temperature.

The reaction product separates into two phases and the upper partcontains the reactants and products, while the lower part containswater, the ionic liquid and the catalyst. The analysis of the productobtained indicates that the conversion under these reaction conditionsand time is 25.2% with a selectivity towards α-terpineol of 47.7%. Theanalysis of lower part shows that the ionic liquid contains water andthe phosphoric acid.

1-10 (canceled)
 11. An ionic liquid comprising: an amine; and an acidic;wherein the amine and the acid are reacted at equimolar proportions,wherein the amine is a tertiaryamines selected from the group consistingof triethylamine, tripropylamine, triisopropylamine, tributylamine,tripentylamine, and mixtures thereof; wherein the ionic liquid is asolvent for hydration reaction of α-pinene to α-terpineol.
 12. The ionicliquid according to claim 11, wherein the acid is an inorganic acidselected from the group consisting of sulfuric acid, phosphoric acid,and mixtures thereof.
 13. The ionic liquid according to claim 11,wherein for the hydration reaction of the α-pinene to α-terpineol, 0.5to 2.5 moles of ionic liquid are used for each mole of pinene.
 14. Theionic according to claim 11, wherein the hydration reaction of theα-pinene to α-terpineol further includes the use of 2-12 moles of waterfor each mole of pinene.
 15. The ionic liquid according to claim 11,wherein the hydration reaction of the α-pinene to α-terpineol includes0.10 to 0.40 moles of the acid used as catalyst for each mole of pinene.16. The ionic liquid according to claim 11, wherein the ionic acidfurther includes an inorganic acid catalyst such as sulfuric acid orphosphoric acid.
 17. A method for producing α-terpineol from α-pinene,the method comprising the steps of: forming an ionic acid by reactingwhile stirring an amine with an acidic, a catalyst, and water; whereinthe amine and the acid are reacted at equimolar proportions, wherein theamine is a tertiaryamines selected from the group consisting oftriethylamine, tripropylamine, triisopropylamine, tributylamine,tripentylamine, and mixtures thereo; using the ionic acid as solvent fora hydration reaction of α-pinene to α-terpineol.
 18. The method of claim17, wherein the reaction is performed at temperatures ranging from roomtemperature to 80° C.
 19. The method according to claim 17, wherein thereaction times ranges from one hour to 36 hours.
 20. The methodaccording to claim 17, further including the step of: cooling the ionicacid; stopping the stirring; wherein an upper and a lower phase areformed, the upper phase contains the α-terpineol and the lower phasecontains the ionic liquid, the catalyst, and the water that did notreact.
 21. The ionic liquid according to claim 20, wherein the catalystand liquid ionic are reused.